Having recently started the CCNA, as it is included in my degree course, and enrolled in the Cisco Network Academy Program, our lecturer has said that the Cisco books for semesters 1-4, although recommended are not a requirement, as all available material is on-line, which it is.

But the problem arises with continuous on-line study. It is very demanding and it is easy to get distracted and go off surfing somewhere. Also, it is the only course that I have been involved in where frequent breaks are recommended, for a smoke coffee etc, except when involved with practical Lab Work. I have purchased the companion guide for the course, as I find it is easier to refer to than the on-line material, it also reinforces what has been studied on-line, and as i don't have a laptop, I can read on the bus etc.
I think my point is, on a personal level, on-line study combined with more conventional methods works best for me